Technical Field
The present disclosure relates to a pen-type position indicator having a function of detecting the writing pressure and a position detecting device configured to be equipped with the position indicator.
Description of the Related Art
A coordinate input device is used as an input device of an information processing device such as a personal computer. For example, the coordinate input device may comprise a pen-type position indicator and a position detecting device having an input surface to which pointing operation and input of characters, figures, and so forth are carried out by using this position indicator. For example, in the case of carrying out design or layout by using a personal computer and the coordinate input device, a user may wish to vary the width of the input line. In this case, by detecting the pressure (writing pressure) applied by the user in the position indicator and transmitting it to the position detecting device, input of information (e.g., line width) according to the writing pressure of the user is enabled. For the detection of the writing pressure applied by the user in the position indicator, a variable-capacitance capacitor described in Patent Document 1 is used conventionally.
FIGS. 8A and 8B show the schematic configuration of a variable-capacitance capacitor 100 disclosed in Patent Document 1. The variable-capacitance capacitor 100 has a dielectric 101 having a substantially circular disc shape, a first electrode 102 attached to one surface (first surface) 101a of the dielectric, and a second electrode 103 that is disposed on the side of a surface (second surface) 101b of the dielectric 101 opposite of the first surface 101a, with the intermediary of a ring-shaped spacer 104 and has flexibility. A first terminal 108 is coupled to the first electrode 102 and a second terminal 109 is coupled to the second electrode 103. On the side of the surface of the second electrode 103 on the opposite side to the surface opposed to the dielectric 101, a substantially rod-shaped or cylindrical-shaped core body 300 continuous with the pen tip of the position indicator is disposed with the intermediary of an elastic body 105.
In the variable-capacitance capacitor 100 having such a configuration, in the state in which the writing pressure of the user is not applied to the pen tip (initial state), the state in which the second surface 101b of the dielectric 101 and the second electrode 103 are separated by the spacer 104 is kept (FIG. 8A). For this reason, an air layer 600 corresponding to the thickness of the spacer 104 is formed between the second surface 101b of the dielectric 101 and the second electrode 103. The electrical capacitance between the first terminal 108 and the second terminal 109 at this time is a series combined capacitance of the electrical capacitance possessed by the dielectric 101 and the electrical capacitance possessed by the air layer 600 with a relative permittivity of, for example, 1.0, and is considerably low.
In contrast, when the writing pressure of the user is applied to the pen tip, the core body 300 is displaced toward the dielectric 101 according to the writing pressure. Thus, the second electrode 103 curves toward the dielectric 101 and gets closer to the dielectric 101. In this case, the electrical capacitance of the air layer 600 becomes higher in inverse proportion to the thickness thereof and the electrical capacitance between the first terminal 108 and the second terminal 109 becomes higher. Thereafter, when the second electrode 103 contacts the second surface 101b of the dielectric 101 as shown in FIG. 8B, the electrical capacitance between the first terminal 108 and the second terminal 109 increases in proportion to the contact area between the other surface 101b of the dielectric 101 and the second electrode 103. Therefore, the pressure (writing pressure) applied to the pen tip continuous with the core body 300 can be detected by detecting change in the electrical capacitance between the first terminal 108 and the second terminal 109.
As above, in the position indicator, the first electrode is attached to one surface (first surface) of the dielectric and the second electrode is disposed on the side of the other surface (second surface) in an opposed manner. Furthermore, the second electrode is pressed against the second surface of the dielectric by the core body according to the writing pressure to form the variable-capacitance capacitor. In this case, the writing pressure may be detected due to change in the electrical capacitance of this capacitor, which changes depending on the contact area between the second surface of the dielectric and the second electrode pressed against it according to the writing pressure.
Regarding the variable-capacitance capacitor for writing pressure detection of the position indicator, various improvements have been made for the purpose of simplification of the configuration, enhancement in the sensitivity of the writing pressure detection, and so forth. FIGS. 9A to 12B are diagrams illustrating improved variable-capacitance capacitors for writing pressure detection of the position indicator. For example, in Patent Document 2, a variable-capacitance capacitor 100A shown in FIG. 9A is disclosed. In the variable-capacitance capacitor 100A, a first electrode 102 is attached to a first surface 101a of a dielectric 101 and a first terminal 108 is coupled to the first electrode 102. A line-shaped second electrode 103 having a part in which the tip is formed into a circular shape is attached to a second surface 101b of the dielectric and a second terminal is coupled to this second electrode 103.
Moreover, a core body 300 continuous with the pen tip is disposed opposed to the second surface 101b of the dielectric 101 and this core body 300 has an electrically-conductive rubber part 300a having, e.g., a dome shape at the end part on the opposite side to the pen tip. Therefore, when the electrically-conductive rubber part 300a makes contact with the second surface 101b of the dielectric 101, the electrically-conductive rubber part 300a also functions as the second electrode. The variable-capacitance capacitor 100A of this example has initial capacitance C0 because the second electrode 103 is already attached to the second surface 101b of the dielectric 101.
When a writing pressure by a user is applied to the pen tip of the position indicator, the electrically-conductive rubber part 300a provided at the end part of the core body 300 continuous with the pen tip on the opposite side to the pen tip moves toward the dielectric 101. The electrically-conductive rubber part 300a contacts the second electrode 103 attached to the second surface of the dielectric 101 in this manner, and collapses, so that the contact area with the second surface of the dielectric 101 becomes larger. This changes the electrical capacitance between the first electrode 102 and the second electrode 103, and the writing pressure may be detected according to this.
In the case of the variable-capacitance capacitor 100A, as shown in a writing pressure detection characteristic of FIG. 9B, the variable-capacitance capacitor 100A has the initial capacitance C0 even in the state in which the writing pressure is not applied, which allows the writing pressure to be detected by lightly applying a force to the pen tip. However, because the initial rise is improved by the function of the second electrode 103 attached to the second surface 101b of the dielectric 101, the range in which the writing pressure can be accurately detected becomes a range on the upper side of a dotted line shown in FIG. 9B, so that the resolution of the writing pressure decreases.
In Patent Document 3, a variable-capacitance capacitor 100B shown in FIG. 10A is disclosed. In the variable-capacitance capacitor 100B, a first electrode 102 is attached to a first surface 101a of a dielectric 101 and a first terminal 108 is coupled to this first electrode 102. Moreover, a core body 300 continuous with the pen tip is disposed opposed to a second surface 101b of the dielectric 101. This core body 300 has an electrically-conductive rubber part 300b having, e.g., a dome shape at the end part on the opposite side to the pen tip and a second terminal 109 is coupled to this electrically-conductive rubber part 300b. Therefore, it is not until the electrically-conductive rubber part 300b contacts the second surface 101b of the dielectric 101 that the electrically-conductive rubber part 300b functions as a second electrode to form the variable-capacitance capacitor.
Furthermore, when a writing pressure by a user is applied to the pen tip of the position indicator, the electrically-conductive rubber part 300b provided at the end part of the core body 300 continuous with the pen tip on the opposite side to the pen tip moves toward the dielectric 101. Thereafter, the electrically-conductive rubber part 300b contacts the second surface of the dielectric 101 and collapses, so that the contact area with the second surface of the dielectric 101 becomes larger. This changes the electrical capacitance between the first electrode 102 and the second electrode 103, and the writing pressure may be detected according to this change. In the case of the variable-capacitance capacitor 100B, the electrical capacitance changes according to the contact area between the second surface 101b of the dielectric 101 and the electrically-conductive rubber part 300b as the second electrode. For this reason, by using the variable-capacitance capacitor 100B, the writing pressure can be accurately detected in a wide range from a light writing pressure to a heavy writing pressure as shown in a writing pressure detection characteristic of FIG. 10B.
However, as is understood through comparison between the writing pressure detection characteristics of FIG. 9B and FIG. 10B, in the case of the variable-capacitance capacitor 100B, the slope of the initial rise is small compared with the variable-capacitance capacitor 100A. To detect the writing pressure only when a pressure is applied by the user, the electrical capacitance of the variable-capacitance capacitor 100B needs to be raised to a determined writing pressure detection threshold over which it can be determined that the writing pressure is being surely applied. However, the slope of the writing pressure detection characteristic is small as shown in FIG. 10B. For this reason, a determined amount of load (writing pressure) needs to be applied until the electrical capacitance of the variable-capacitance capacitor 100B increases to the writing pressure detection threshold. Thus, the initial rise sensitivity is lowered (becomes dull) compared with the variable-capacitance capacitor 100A shown in FIG. 9A.
For this reason, it is conceivable that, as shown in FIG. 11A, an electrically-conductive rubber part 300c whose tip is flattened to have a certain amount of area is provided at the end part of the core body 300 on the opposite side to the pen tip. In a variable-capacitance capacitor 100C, the respective parts other than the electrically-conductive rubber part 300c are formed similarly to the variable-capacitance capacitor 100B shown in FIG. 10A. In the case of the variable-capacitance capacitor 100C, when the second surface 101b of the dielectric 101 contacts the electrically-conductive rubber part 300c, the contact is made with a determined area from the beginning.
For this reason, in the case of the variable-capacitance capacitor 100C, a characteristic in which the initial rise is early can be made as shown in writing pressure detection characteristics of FIG. 11B. However, in the case of the variable-capacitance capacitor 100C, the initial rise is improved by flattening the tip part of the electrically-conductive rubber part 300c and thus the range in which the writing pressure can be accurately detected becomes a range on the upper side of a dotted line shown in FIG. 11B. Therefore, also in the variable-capacitance capacitor 100C shown in FIG. 11A, the resolution of the writing pressure decreases similarly to the case of the variable-capacitance capacitor 100A shown in FIG. 9A.
Furthermore, in the case of the variable-capacitance capacitor 100C shown in FIG. 11A, the tip of the end part of the electrically-conductive rubber part 300c on the opposite side to the pen tip is flattened as described above. For this reason, under the influence of the attaching state of the electrically-conductive rubber part 300c and so forth, how the electrically-conductive rubber part 300c contacts the second surface part of the dielectric 101 differs for each position indicator equipped with the variable-capacitance capacitor 100C. Therefore, as shown by the three writing pressure detection characteristics in FIG. 11B, there is a case in which variation is caused in the initial rise rate of the writing pressure detection characteristic for each position indicator equipped with this variable-capacitance capacitor 100C.
This possibly occurs also in the same position indicator equipped with this variable-capacitance capacitor 100C. Specifically, variation may occur in the initial rise rate according to how the electrically-conductive rubber part 300c contacts the second surface part 101b of the dielectric 101 differs under the influence of how the position indicator is tilted at the time of use and so forth. In this case, even with the same position indicator, there is a possibility that variation is caused in the touch of writing for every use.
In Patent Document 4, a variable-capacitance capacitor 100D shown in FIG. 12A is disclosed. In the variable-capacitance capacitor 100D, a first electrode 102 is attached to a first surface 101a of a dielectric 101 and a first terminal 108 is coupled to this first electrode 102. On the side of a second surface 101b of the dielectric 101, a second electrode 103a that has flexibility and has an extending part extending from the center in a radial manner is disposed with the intermediary of a ring-shaped spacer although the spacer is not shown in the diagram. A second terminal 109 is coupled to the second electrode 103a. The second electrode 103a has a so-called ribbon shape. On the side of the surface of the second electrode 103a on the opposite side to the surface opposed to the dielectric 101, a rod-shaped core body 300 continuous with the pen tip of the position indicator is disposed with the intermediary of an elastic body although the elastic body is not shown in the diagram.
That is, the variable-capacitance capacitor 100D shown in FIG. 12A has a configuration similar to that of the variable-capacitance capacitor 100 described by using FIGS. 8A and 8B except for that the shape of the second electrode 103 is different. In the case of the variable-capacitance capacitor 100D, the slope of the writing pressure detection characteristic can be adjusted depending on the shape of the second electrode as shown in writing pressure detection characteristics of FIG. 12B for example.
Specifically, the slope can be made smaller when the area of the extending part extending from the center of the second electrode 103a in a radial manner is set smaller, and the slope can be made larger when the area of this extending part is set larger. This can change the so-called touch of writing. However, when the slope of the writing pressure detection characteristic is made smaller, the detection sensitivity of the writing pressure becomes duller although the resolution of the writing pressure increases. Conversely, when the slope of the writing pressure detection characteristic is made larger, the resolution of the writing pressure decreases although the detection sensitivity of the writing pressure becomes sharper.
As above, in the position indicator, various improvements are made in order to enhance the degree of satisfaction of the user regarding the variable-capacitance capacitor for detecting the writing pressure of the user. However, the relationship between the detection sensitivity of the writing pressure and the resolution of the writing pressure is a so-called trade-off relationship. Furthermore, as described by using FIGS. 11A and 11B, there is also the variable-capacitance capacitor involving an inconvenience that variation is possibly caused in the initial rise rate because of its configuration.